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Can't find flat top pistons


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Hi,

 

As the title said, I' m looking for L28 .020 oversized flat top piston. I am building an NA L28 and I want the flat top piston for higher compression ratio. All I can find are ITM piston. I dont know this brand and I want to be sure of what I buy first, since the engin will be floored very, very often.

 

Anyone who had the same trouble?

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ITM pistons are fine for stock rpm range. Their design is similar to stock units.

I run NA L28 with max power at 6500rpm max (if not lower) so ITM pistons are fine.

 

If you're looking for high rpm operation, you might want some lighter units. Custom forged pistons are probably more appropriate.

 

Being at WOT or not, does not make any difference for pistons. Accel is what's killing pistons due to mass and inertia. piston acceleration is a function of engine rpm.

Stress because of pressure due to fuel burn is much lower than load/stress due to inertia.

Edited by Lazeum
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That is well explain, thank you.

My expectation were max 7000 rpm... The ITM pistons are 300$ delivered, costum forged piston is more like 900$. My plan was to put triple mukunis next winter. What do you think I should do? I think I'll buy the ITM.

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Max 7000rpm usually means max power around 6500rpm.

You're at the limit for ITM pistons but it should be fine.

Think also about what you'd like to do in the future. Some, here, have some regrets because they would like to upgrade parts to get more power at high rpm but they've chosen ITM pistons, they are limited. 

 

Thinking about pistons is fine but going at high rpm above 7000rpm means also some extra investments: damper able to hold at +7000rpm, fully balance system including pistons, crank, rods, flywheel, clutch, etc. 

It also means camshaft able to use the power band. It should come then with special springs for high lift, lash pad with very specific thickness, major head work to be able to breath at that rpm level, lube system up to the task for rpm operation, ignition able to operate at high rpm, big enough carbs, etc. etc.

 

My point is $600 difference between pistons is just one small parameters between many others that make an engine to cost $3000 or $10000.

 

I've got a stock (but carefully built) bottom end with lube system upgraded (turbo high flow oil pump, oil restrictor enlarged), prep'ed head done to match my camshaft specifications and CR, good ignition system, good exhaust, sidedraft carbs. The car on open roads is really nice to drive with lot of torque and power. It is not the most powerful car in the world but it is way enough to enjoy the car and get major speeding tickets.

Total cost for my engine was around $4000 starting from stock bottom end with new ITM pistons, new gaskets everywhere, port/polished/unshrouded head, Rebello cam, ARP hardware.

 

I've bought all my parts at Clark's Discount. The guy is really nice to deal with, prices are very fair, shipping was super quick (5 days delivery - I'm in France).

Edited by Lazeum
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Je comprends ton point. J'assume que tu comprends le francais ahah. Je fais balancer toute la base de mon bloc, cranck, piston, biele, flywheel et clutch. Je concentre mon argent sur la base, tout sera neuf, seal, bolt, pompe a lhuile etc. Je nai actuellement pas les moyens de mettre plus de 5-6000$. Cest pourquoi je laisse le travail de la tete a plus tard.. Je sais que le plus important a faire est la tete, mais jai acheter un bloc f54 et une tete n42 separer et toute la base est a rebatir. J'ai l'intention de faire n port and polish, tri way valve job, mettre un cam et triple carb. Au fond je souhaite sortir le meilleur possible de mon bloc en restant NA et fiable. Tu me fait hésiter en disant que certains regrettent.

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Of course, I do understand French, it is somehow my native language :)

Rule of the forum is to speak in English, so I do it (I've lived many years in the US so that's no problem)

 

The head is definitely the main part of the build. You'll see on the board that reliability comes from the bottom end, power from the top part of the engine.

My head work with hardware was not cheap (above $2000) but difference with previous stock head was huge.

 

When I told you some regrets having ITM pistons, it is because some want always more. At some point, cast aluminum pistons are going to limit the potential of your build. Since it is not easy to change them, it is something to take into consideration if you ever expect to go above 7000rpm on a regular basis.

As far as I'm concerned, my car is a road car and it fully meets my expectations.

Edited by Lazeum
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Well, i'm sorry for breaking the rules!

 

From the history I have with my past cars, I believe a good torque a low rpm and 200-220 hp is enough for me, all I realy need is an lsd :)

So i guess I'll stay with the itm.

 

Thanks a lot everyone, this was realy helpful!

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Well, i'm sorry for breaking the rules!

 

From the history I have with my past cars, I believe a good torque a low rpm and 200-220 hp is enough for me, all I realy need is an lsd :)

So i guess I'll stay with the itm.

 

Thanks a lot everyone, this was realy helpful!

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  • 2 months later...

OK, I get that ITM are good for stock RPM range (that is all I am aiming for).

 

I have heard that people have had issues with their rings and it has been suggested to get Hasting 2C6142 instead (chrome upper ring).

 

Thoughts, feedback...

 

 

PS. Any hope in the world of finding a set of OEM oversize anywhere? Really hoping someone bought a set, and then decided to go forged when they did their build, and have these available to sell to a good car (mine is a 72 240z that i have owned for 34 years, and am hoping to build a good strong, long lasting engine for).

Edited by rick240zed
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